Generally, a fiber bragg grating (FBG) sensor is a wavelength selective device created by forming a grating that periodically modulates an index of refraction in a glass core of an optical fiber to selectively reflect a specific wavelength.
Since the FBG sensor for measuring physical quantity has good physical properties, for example, it has an inherent wavelength and is not affected by an electromagnetic wave, the FBG sensor substitutes for a conventional electrical gauge. A field of application for the FBG sensor is abruptly increased in recent years.
In spite of a very small diameter of 125 mm, the FBG sensor has a large tension per unit area. Consequently, since the FBG sensor is easily ruptured by an external shock, it is required to exquisitely attach the FBG sensor to buildings or bridges.
In addition, the FBG sensor should be tightly installed to have proper tension, thereby measuring an accurate value. Since there is no proper fixer for the FBG sensor to a civil construction, an experienced engineer should directly set a value of the FBG sensor in a site, which is limited in space-time.
As such, although the FBG sensor has a good measuring performance, it is not widely used in various industrial fields, due to difficult installation and manipulation of the FBG sensor.
Meanwhile, the FBG sensor is directly attached to an object to be measured by an adhesive or an optional fixing piece. Therefore, the FBG sensor is likely to be exposed to external circumstances such as rain, wind, bugs or animals.
The FBG sensor exposed to the external circumstances may wrongly measure a strain, so that it is difficult to constantly inspect civil construction and maintain a measuring system.